<template>
  <div class="pagination">
    <!-- 当前页为第一页 不可点 -->
    <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo - 1)">上一页</button>
    <!-- 展示第一页(start) >1 才展示 =1时由中间部分展示-->
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{ active: pageNo == 1 }">1</button>
    <!-- 展示第一页(start) >2 才展示 1 ... 3 4-->
    <button v-if="startNumAndEndNum.start > 2">···</button>
    <!-- 循环展示start - end-->
    <button v-for="(page,index) in startNumAndEndNum.end" :key="index" v-if="page >= startNumAndEndNum.start" @click="$emit('getPageNo',page)" :class="{ active: pageNo == page }">{{page}}</button>
    <!-- 展示最后一页(end) <总数-1 才展示 28 ... 30(总数)-->
    <button v-if="startNumAndEndNum.end < totalPage -1">···</button>
    <!-- 展示最后一页(end) <总数 才展示 =总数时由中间部分展示-->
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)" :class="{ active: pageNo == totalPage }">{{totalPage}}</button>
    <!-- 当前页为最后一页 不可点 -->
    <button :disabled="pageNo == totalPage" @click="$emit('getPageNo',pageNo +1)">下一页</button>
    
    <button style="margin-left: 30px">共 {{total}} 条</button>
  </div>
</template>

<script>
  export default {
    name: "Pagination",
    props:["pageNo","pageSize","total","continues"],
    computed:{
        //总共多少页
        totalPage(){
            //向上取整
            return Math.ceil(this.total/this.pageSize)
        },
        //计算出连续的页码的起始数字与结束数字[连续页码的数字:至少是5]
    startNumAndEndNum() {
      const { continues, pageNo, totalPage } = this;
      //先定义两个变量存储起始数字与结束数字
      let start = 0,
        end = 0;
      //连续页码数字5【就是至少五页】，如果出现不正常的现象【就是不够五页】
      //不正常现象【总页数没有连续页码多】
      if (continues > totalPage) {
        start = 1;
        end = totalPage;
      } else {
        //正常现象【连续页码5，但是你的总页数一定是大于5的】
        //起始数字
        start = pageNo - parseInt(continues / 2);
        //结束数字
        end = pageNo + parseInt(continues / 2);
        //把出现不正常的现象【start数字出现0|负数】纠正
        if (start < 1) {
          start = 1;
          end = continues;
        }
        //把出现不正常的现象[end数字大于总页码]纠正
        if (end > totalPage) {
          end = totalPage;
          start = totalPage - continues + 1;
        }
      }
      return { start, end };
    },
    }
  }
</script>

<style lang="less" scoped>
  .pagination {
      text-align:center;
    button {
      margin: 0 5px;
      background-color: #f4f4f5;
      color: #606266;
      outline: none;
      border-radius: 2px;
      padding: 0 4px;
      vertical-align: top;
      display: inline-block;
      font-size: 13px;
      min-width: 35.5px;
      height: 28px;
      line-height: 28px;
      cursor: pointer;
      box-sizing: border-box;
      text-align: center;
      border: 0;

      &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
      }

      &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
      }
    }
  }
</style>
